Authorities carried out arbitrary detentions, torture and use of indiscriminate force, Amnesty says in new report.

Nicaraguan authorities have carried out arbitrary detentions and torture and used lethal force against anti-government protesters as part of a "intensified strategy for repression", Amnesty International said on Thursday.

In a new report, the rights organisation documented several cases in which police forces and pro-government paramilitary groups committed extrajudicial executions, as well as used of "weapons of war" on protesters.

"Not only did President (Daniel) Ortega deploy police to arbitrarily arrest and torture demonstrators, he also used heavily armed pro-government groups to kill, wound and intimidate all those brave enough to stand up to his repressive strategy," said Erika Guevara-Rosas, Amnesty's America director.

The unrest in Nicaragua began in mid-April after Ortega introduced non-scrapped pension reform plans. Since then, they have grown into widespread protests, calling for the president and his wife, Vice President Rosario Murillo, to step down.

Rights groups say more than 300 people have been killed and hundreds of others arrested during the violence. The government disputes the figures, saying around 200 people have died.

Ortega has also dismissed UN charges of disproportionate use of force against protesters, enforced disappearances and torture.

He called the UN a tool of "lies and infamy", and last month expelled the UN rights mission after it published a report criticising the "climate of fear" in the country.

'Executions as punishment'

Amnesty documented cases that it said appeared to be extrajudicial executions, which were carried out as a form of punishment.

Among the cases examined was that of Faber Lopez Vivas, a National Riot Police officer, who was critical of the behaviour of his department. Lopez Vivas was found dead in July. The National Police said the officer was shot dead by "armed terrorists", but in an interview with Amnesty, Lopez Vivas's family said the officer had no bullet wounds and a private pathologist reported there were multiple signs of torture. Amnesty said his family believes he was executed by police as a form of punishment.

"This is a severe crisis," Pilar San Martin, crisis researcher for the Americas in Amnesty International said.

"We documented different elements of this new strategy carried out by the government, where we could see a strategy of repression that has been intensified.

"From June, we could see the use of military weapons [against civilians], this is one of the elements that allow us to say that the strategy has been intensified," she added.

The rights organisation documented at least 12 cases of possible torture, the report said, including one case of sexual torture against a young woman who had been detained. The report also noted several cases of probable arbitrary arrests and violations of due process that Amnesty said "formed part of the government's strategy to break up the protest movement".

Last weekend, dozens of people were arrested ahead of a planned march against Ortega, which was cancelled after the detention. AFP reported at least 30 people were released earlier this week. According to the news agency, local human rights groups welcomed the release but said another 500 people also arrested after protesting again the government are still in prison.

"We don't know where [or when] will this end," San Martin from Amnesty said on Thursday, but "we are calling on the government to stop this crackdown, and the excessive use of force against the protesters."